The present invention relates to clothes washing machines and more particularly to a washing machine driven by a DC electronically commutated motor (ECM), for example, of the type disclosed in U.S. Pat. No. 4,329,630 assigned to the General Electric Company, the assignee of the present invention.
Motors of this type are bi-directional, capable of producing relatively slow oscillation of the agitator during the wash cycle with the motor being cyclically reversed and relatively high speed unidirectional spinning of the basket during an extraction cycle. Both types of motions are implemented by means of appropriate control of the voltage and current applied to the winding of the motor. At the end of each direction of rotation, the motor is electronically braked to terminate basket rotation. The dynamic braking of the motor is acting, in effect, against the velocity and inertia generated by the mass of the high speed spinning of the basket.
During the washing operation, when the motor is cyclically reversed the inertia of the basket is not a significant factor in the electronic braking of the motor between oscillatory directions. During the high speed unidirectional spin extraction cycle, the basket is rotated at speeds of approximately 600 RPM. At this speed the inertia generated by the mass of the high speed spinning basket may place too much resistance to the dynamic braking capability of the electronically commutated motor.
In prior art machines employing conventional motors, the spin extraction cycle is terminated by de-energizing the motor, at which time the basket mass wants to continue to rotate as a result of its inertia. Since access to the basket while it is still rotating presents a danger to the consumer, it is imperative that rotation of the basket stop at the time the motor is de-energized. It has been customary to provide some form of mechanical braking to accomplish adequate braking. This generally requires a special braking mechanism in addition to the motor and transmission which adds to the overall cost and complexity of the machine.
By the present invention, the size and design of the electronically commutated motor are selected to accomplish the braking of the basket under most operating conditions. However, means are provided to assist and supplement motor braking under all operating conditions.